Portable coordinate measurement machine

ABSTRACT

A portable coordinate measurement machine comprises an articulated arm having jointed arm segments. The arm includes joint assemblies which include at least one read head together with one or more (preferably five) sensors (preferably proximity sensors) in communication with a periodic pattern of a measurable characteristic, the pattern and read heads being positioned within the joint so as to be rotatable with respect to each other.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of provisional applicationNo. 60/357,599 filed Feb. 14, 2002 and 60/394,908 filed Jul. 10, 2002,all of the contents of both provisional applications being incorporatedherein by reference and is a continuation-in-part of application Ser.No. 10/366,589 filed Feb. 13, 2003.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates in general to coordinate measurementmachines (CMMs) and in particular to portable CMMs having an articulatedarm.

[0004] 2. Prior Art

[0005] Currently, portable articulated arms are provided as ameasurement system with a host computer and applications software. Thearticulated arm is commonly used to measure points on an object andthese measured points are compared to computer-aided design (CAD) datastored on the host computer to determine if the object is within the CADspecification. In other words, the CAD data is the reference data towhich actual measurements made by the articulated arm are compared. Thehost computer may also contain applications software that guides theoperator through the inspection process. For many situations involvingcomplicated applications, this arrangement is appropriate since the userwill observe the three-dimensional CAD data on the host computer whileresponding to complex commands in the applications software.

[0006] An example of a prior art portable CMM for use in theabove-discussed measurement system is disclosed in U.S. Pat. No.5,402,582 ('582), which is assigned to the assignee hereof andincorporated herein by reference. The '582 patent discloses aconventional three-dimensional measuring system composed of a manuallyoperated multi-jointed articulated arm having a support base on one endthereof and a measurement probe at the other end. A host computercommunicates to the arm via an intermediate controller or serial box. Itwill be appreciated that in the '582 patent, the arm will electronicallycommunicate with the serial box which, in turn, electronicallycommunicates with the host computer. Commonly assigned U.S. Pat. No.5,611,147 ('147), which is again incorporated herein by reference,discloses a similar CMM having an articulated arm. In this patent, thearticulated arm includes a number of important features including anadditional rotational axis at the probe end thus providing for an armwith either a two-one-three or a two-two-three joint configuration (thelatter case being a 7 axis arm) as well as improved pre-loaded bearingconstructions for the bearings in the arm.

[0007] Still other relevant prior art CMMs include commonly assignedU.S. Pat. No. 5,926,782 ('782), which provides an articulated arm havinglockable transfer housings for eliminating one or more degrees offreedom and U.S. Pat. No. 5,956,857 ('857) which provides an articulatedarm having a quick disconnect mounting system.

[0008] More current portable CMMs of the type described herein do notnecessitate the use of an intermediate controller or serial box sincethe functionality thereof is now incorporated in the software providedby the host computer. For example, commonly assigned U.S. Pat. No.5,978,748 ('748), which is incorporated herein by reference, disclosesan articulated arm having an on-board controller which stores one ormore executable programs and which provides the user with instructions(e.g., inspection procedures) and stores the CAD data that serves as thereference data. In the '748 patent, a controller is mounted to the armand runs the executable program which directs the user through a processsuch as an inspection procedure. In such a system, a host computer maybe used to generate the executable program. The controller mounted tothe arm is used to run the executable program but cannot be used tocreate executable programs or modify executable programs. By way ofanalogy to video gaming systems, the host computer serves as theplatform for writing or modifying a video game and the arm mountedcontroller serves as the platform for playing a video game. Thecontroller (e.g., player) cannot modify the executable program. Asdescribed in the '748 patent, this results in a lower cost threedimensional coordinate measurement system by eliminating the need for ahost computer for each articulated arm. U.S. application Ser. No.09/775,236 ('236), assigned to the assignee hereof and incorporatedherein by reference, discloses a method and system for deliveringexecutable programs to users of coordinate measurement systems of thetype disclosed in the '748 patent. The method includes receiving arequest to create an executable program from a customer and obtaininginformation related to the executable program. The executable program isthen developed which guides an operator through a number of measurementsteps to be performed with the three dimensional coordinate measuringsystem. The executable program is delivered to the customer, preferablyover an on-line network such as the Internet.

[0009] Commonly assigned U.S. Pat. No. 6,131,299 ('299), (all thecontents of which is incorporated herein by reference), discloses anarticulated arm having a display device positioned thereon to allow anoperator to have convenient display of positional data and system menuprompts. The display device includes for example, LEDs which indicatesystem power, transducer position status and error status. U.S. Pat. No.6,219,928 ('928), which is assigned to the assignee and incorporatedherein by reference, discloses a serial network for the articulated arm.The serial network communicates data from transducers located in the armto a controller. Each transducer includes a transducer interface havinga memory which stores transducer data. The controller serially addresseseach memory and the data is transferred from the transducer interfacememory to the controller. Commonly assigned U.S. Pat. No. 6,253,458('458) and U.S. Pat. No. 6,298,569 ('569) both disclose adjustablecounter balance mechanisms for articulated arm portable CMMs of the typedescribed herein.

[0010] While well suited for their intended purposes, there is acontinued and perceived need in the industry for improved portable CMMsthat are easier to use, more efficient to manufacture, provide improvedfeatures and can be sold at a lower cost.

SUMMARY OF THE INVENTION

[0011] In accordance with the present invention, a portable CMMcomprises an articulated arm having jointed arm segments. In oneembodiment, the arm segments include bearing/encoder cartridges whichare attached to each other at predetermined angles using a dual socketjoint. Each cartridge contains at least one, and preferably two,preloaded bearing assemblies and an encoder, preferably an opticalencoder, all assembled in a cylindrical housing. Preferably, two or moreencoder read heads are used in each joint so as to cause cancellationeffects that can be averaged. The arm segments may be threadablyinterconnected with the arm tapering from a wider diameter at its baseto a narrower diameter at the probe end.

[0012] In accordance with another embodiment of the present invention,one or more of the jointed arm segments of the articulated arm includesreplaceable protective coverings and/or bumpers to limit high impactshock and abrasion as well as to provide an ergonomically andaesthetically pleasing gripping location.

[0013] In still another embodiment of this invention, the articulatedarm includes an integrated, internal counter balance in one of the hingejoints. This counter balance utilizes a coil spring having relativelywide end rings and narrower internal rings machined from a metalcylinder. The spring further includes at least two (and preferablythree) posts for locking into the hinge structure of the arm as well asa spring adjustment mechanism.

[0014] In still another embodiment of this invention, the articulatedarm includes a measurement probe at one end thereof. This measurementprobe has an integrally mounted touch trigger probe which is easilyconvertible to a conventional hard probe. The measurement probe alsoincludes improved switches and a measurement indicator light. In oneembodiment, the switches have an arcuate, oblong shape and are easilyarctuatable by the operator. The improved switches include differingcolor, surface texture and/or height which allow the operator to easilydistinguish between them while the indicator light preferably iscolor-coded for ease of operation.

[0015] Another embodiment of the present invention includes anarticulated arm having an integral, on-board power supply rechargerunit. This power supply/recharger unit allows for a fully portable CMMand makes it far easier to use the CMM at a remote location and/orwithout the need for a directly cabled articulated arm.

[0016] Still another embodiment of the present invention includes anarticulated arm having a measurement probe at one end. The measurementprobe includes a rotatable handle cover and switch assembly whichsurrounds the measurement probe. The rotatable handle cover and switchassembly allows the measurement probe to be more easily held andactivated regardless of hand position. The use of the rotatable handlecover further precludes the necessity for having a third axis ofrotation at the probe end thus allowing for a lower cost and more easilyconstructed portable CMM (relative to 7 axis CMMs or CMMs having a thirdangle of rotation at the measurement probe).

[0017] In another embodiment of this invention, a portable CMM includesan articulated arm having jointed arm segments with a measurement probeat one end thereof and a base at the other end thereof. In accordancewith a novel feature of this embodiment, the base has an integratedmagnetic mount therein for attaching the arm to a magnetic surface. Thisintegrated magnetic mount is preferably threadably connected to thearticulated arm and has an on/off lever for ease of use (which leverpreferably automatically engages when the mount is positioned onto amagnetic surface).

[0018] The above-discussed and other features and advantages of thepresent invention will be appreciated and understood by those skilled inthe art from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Referring now to the drawings wherein like elements are numberalike in the several FIGURES:

[0020]FIG. 1 is a front perspective view of the portable CMM of thepresent invention including an articulated arm and attached hostcomputer;

[0021]FIG. 2 is a rear perspective view of the CMM of FIG. 1;

[0022]FIG. 3 is a right side view of the CMM of FIG. 1 (with the hostcomputer removed);

[0023]FIG. 3A is a right side view of the CMM of FIG. 1 with slightlymodified protective sleeves covering two of the long joints;

[0024]FIG. 4 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base and the first articulated armsection;

[0025]FIG. 5 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base, first arm section and partiallyexploded second arm section;

[0026]FIG. 6 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base, first arm section, second armsection and partially exploded third arm section;

[0027]FIG. 7 is an exploded, perspective view depicting a pair ofencoder/bearing cartridges being assembled between two dual socketjoints in accordance with the present invention;

[0028]FIG. 8 is a front elevation view of the bearing/encoder cartridgesand dual socket joints of FIG. 7;

[0029]FIG. 9 is an exploded, perspective view of a short bearing/encodercartridge in accordance with the present invention;

[0030]FIG. 9A is an exploded, perspective view similar to FIG. 9, butshowing a single read head;

[0031]FIG. 9B is an exploded, perspective view, similar to FIG. 9, butshowing four read heads;

[0032]FIG. 9C is a perspective view of FIG. 9B after assembly;

[0033]FIG. 9D is an exploded, perspective view, similar to FIG. 9, butshowing three read heads;

[0034]FIG. 9E is a perspective view of FIG. 9D after assembly;

[0035]FIG. 10 is a cross-sectional elevation view of the cartridge ofFIG. 9;

[0036]FIG. 11 is an exploded, perspective view of a long bearing/encodercartridge in accordance with the present invention;

[0037]FIG. 11A is an exploded, perspective view similar to FIG. 11, butshowing a single read head;

[0038]FIG. 12 is a cross-sectional elevation view of the cartridge ofFIG. 11;

[0039]FIG. 12A is a cross-sectional elevation view of the cartridge ofFIG. 12 depicting the dual read heads being rotatable with the shaft;

[0040]FIG. 13 is an exploded, perspective view of still anotherbearing/encoder cartridge in accordance with the present invention;

[0041]FIG. 13A is an exploded, perspective view similar to FIG. 13, butshowing a single read head;

[0042]FIG. 14 is a cross-sectional elevation view of the cartridge ofFIG. 13;

[0043]FIG. 15 is an exploded, perspective view of a bearing/encodercartridge and counter balance spring in accordance with the presentinvention;

[0044]FIG. 15A is an exploded, perspective view similar to FIG. 15, butshowing a single read head;

[0045]FIG. 16 is a cross-sectional elevation view of the cartridge andcounter balance of FIG. 15;

[0046]FIG. 17 is a top plan view of a dual read head assembly for alarger diameter bearing/encoder cartridge used in accordance with thepresent invention;

[0047]FIG. 18 is a cross-sectional elevation view along the line 18-18of FIG. 17;

[0048]FIG. 19 is a bottom plan view of the dual read head assembly ofFIG. 17;

[0049]FIG. 20 is a top plan view of a dual read head assembly for asmaller diameter bearing/encoder cartridge in accordance with thepresent invention;

[0050]FIG. 21 is a cross-sectional elevation view along the line 21-21of FIG. 20;

[0051]FIG. 22 is a bottom plan view of the dual read head assembly ofFIG. 20;

[0052]FIG. 23A is a block diagram depicting the electronicsconfiguration for the CMM of the present invention using a single readhead and FIG. 23B is a block diagram depicting the electronicsconfiguration for the CMM of the present invention using a dual readhead;

[0053]FIG. 24 is a cross-sectional elevation view longitudinally throughthe CMM of the present invention (with the base removed);

[0054]FIG. 24A is a cross-sectional elevation view of the CMM of FIG.3A;

[0055]FIG. 25 is an enlarged cross-sectional view of a portion of FIG.24 depicting the base and first long joint segment of the CMM of FIG.24;

[0056]FIG. 25A is a perspective view of the interconnection between along and short joint in accordance with an alternative embodiment of thepresent invention;

[0057]FIG. 25B is a cross-sectional elevation view longitudinallythrough a portion of FIG. 25A;

[0058]FIG. 26 is an enlarged cross-sectional view of a portion of FIG.24 depicting the second and third long joint segments;

[0059]FIGS. 26A and B are enlarged cross-sectional views of portions ofFIG. 24A depicting the second and third long joints as well as theprobe;

[0060]FIG. 27A is an exploded side elevation view depicting the firstshort joint/counter balance assembly in accordance with the presentinvention;

[0061]FIG. 27B is a perspective view depicting the components of FIG.27A;

[0062]FIG. 28 is a cross-sectional elevation view depicting the internalcounter balance of the present invention;

[0063]FIG. 29 is a cross-sectional, side elevation view through a firstembodiment of the measurement probe in accordance with the presentinvention;

[0064]FIG. 29A is a side elevation view of another embodiment of ameasurement probe in accordance with the present invention;

[0065]FIG. 29B is a cross-sectional elevation view along the line29B-29B of FIG. 29A;

[0066]FIG. 29C is a perspective view of a pair of “take” or “confirm”switches used in FIGS. 29A-B;

[0067] FIGS. 30A-C are sequential elevation plan views depicting theintegrated touch probe assembly and conversion to hard probe assembly inaccordance with the present invention;

[0068]FIG. 31 is a cross-sectional, side elevation view through stillanother embodiment of a measurement probe in accordance with the presentinvention;

[0069]FIG. 32 is an exploded, perspective view of the integratedmagnetic base in accordance with the present invention;

[0070]FIG. 33 is a cross-sectional elevation view through the magneticbase of FIG. 32;

[0071]FIG. 34 is a top plan view of the magnetic mount of FIG. 32;

[0072]FIG. 35 is a cross-sectional elevation view of a CMM joint fromRaab '356 with dual read heads;

[0073]FIG. 36 is a cross-sectional elevation view of a CMM joint fromEaton '148 with

[0074] dual read heads;

[0075]FIG. 37 is a side elevation view of a measurement probe with aseventh axis transducer;

[0076]FIG. 38 is a side elevation view, similar to FIG. 37, butincluding a removable handle;

[0077]FIG. 39 is an end view of the measurement probe of FIG. 38;

[0078]FIG. 40 is a cross-sectional elevation view of the measurementprobe of FIG. 38;

[0079]FIG. 41 is a top plan view of a bearing/encoder cartridgeemploying a read head combined with a plurality of sensors in accordancewith the present invention;

[0080]FIG. 42 is a perspective view of the cartridge of FIG. 41; and

[0081]FIG. 43 is an enlarged view of the upper portion of the cartridgeof FIG. 42.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0082] Referring first to FIGS. 1-3, the CMM of the present invention isshown generally at 10. CMM 10 comprises a multijointed, manuallyoperated, articulated arm 14 attached at one end to a base section 12and attached at the other end to a measurement probe 28. Arm 14 isconstructed of basically two types of joints, namely a long joint (forswivel motion) and a short joint (for hinge motion). The long joints arepositioned substantially axially or longitudinally along the arm whilethe short joints are preferably positioned at 90° to the longitudinalaxis of the arm. The long and short joints are paired up in what iscommonly known as a 2-2-2 configuration (although other jointconfigurations such as 2-1-2, 2-1-3, 2-2-3, etc. may be employed) Eachof these joint pairs are shown in FIGS. 4-6.

[0083]FIG. 4 depicts an exploded view of the first joint pair, namelylong joint 16 and short joint 18. FIG. 4 also depicts an exploded viewof the base 12 including a portable power supply electronics 20, aportable battery pack 22, a magnetic mount 24 and a two-piece basehousing 26A and 26B. All of these components will be discussed in moredetail hereinafter.

[0084] Significantly, it will be appreciated that the diameters of thevarious primary components of articulated arm 14 will taper from thebase 12 to the probe 28. Such taper may be continuous or, as in theembodiment shown in the FIGURES, the taper may be discontinuous orstep-wise. In addition, each of the primary components of articulatedarm 14 may be threadably attached thereby eliminating a large number offasteners associated with prior art CMMs. For example, and as will bediscussed hereafter, magnetic mount 24 is threadably attached to firstlong joint 16. Preferably, such threading is tapered threading which isself-locking and provides for increased axial/bending stiffness.Alternatively, as shown in FIGS. 25A and 25B, and as discussedhereafter, the primary components of the articulated arm may havecomplimentary tapered male and female ends with associated flanges, suchflanges being bolted together.

[0085] Referring to FIG. 5, the second set of a long and short joint isshown being attached to the first set. The second joint set includeslong joint 30 and short joint 32. As is consistent with the attachmentof magnetic mount 24 to long joint 16, long joint 30 is threadablyattached to threading on the interior surface of long joint 16.Similarly, and with reference to FIG. 6, the third joint set includes athird long joint 34 and a third short joint 36. Third long joint 34threadably attaches to threading on the interior surface of second shortjoint 32. As will be discussed in more detail hereinafter, probe 28threadably attaches to short joint 36.

[0086] Preferably, each short joint 18, 32 and 36 is constructed of castand/or machined aluminum components or alternatively, lightweight stiffalloy or composite. Each long joint 16, 30 and 34 is preferablyconstructed of cast and/or machined aluminum, lightweight stiff alloyand/or fiber reinforced polymer. The mechanical axes of the threeaforementioned joint pairs (i.e., pair 1 comprises joint pairs 16, 18,pair 2 comprises joint pairs 30, 32 and pair 3 comprises joint pairs 34,36) are aligned with respect to the base for smooth, uniform mechanicalbehavior. The aforementioned tapered construction from base 12 to probe28 is preferred to promote increased stiffness at the base where loadsare greater and smaller profile at the probe or handle whereunobstructed use is important. As will be discussed in more detailhereinafter, each short joint is associated with a protective bumper 38on either end thereof and each long probe is covered with a protectivesleeve 40 or 41. It will be appreciated that the first long joint 16 isprotected by the base housing 26A, B which provides the same type ofprotection as sleeves 40, 41 provide for the second and third longjoints 30, 34.

[0087] In accordance with an important feature of the present invention,each of the joints of the articulated arm utilizes a modularbearing/encoder cartridge such as the short cartridge 42 and the longcartridge 44 shown in FIGS. 7 and 8. These cartridges 42, 44 are mountedin the openings of dual socket joints 46, 48. Each socket joint 46, 48includes a first cylindrical extension 47 having a first recess orsocket 120 and a second cylindrical extension 49 having a second recessor socket 51. Generally, sockets 120 and 51 are positioned 90 degrees toone another although other relative, angular configurations may beemployed. Short cartridge 42 is positioned in each socket 51 of dualsocket joints 46 and 48 to define a hinge joint, while long cartridge 44is positioned in socket 120 of joint 46 (see FIG. 25) and long cartridge44′ (see FIG. 26) is positioned in socket 120 of joint 48 to each definea longitudinal swivel joint. Modular bearing/encoder cartridges 42, 44permit the separate manufacture of a pre-stressed or preloaded dualbearing cartridge on which is mounted the modular encoder components.This bearing encoder cartridge can then be fixedly attached to theexternal skeletal components (i.e., the dual socket joints 46, 48) ofthe articulated arm 14. The use of such cartridges is a significantadvance in the field as it permits high quality, high speed productionof these sophisticated subcomponents of articulated arm 14.

[0088] In the embodiment described herein, there are four differentcartridge types, two long axial cartridges for joints 30 and 34, onebase axial cartridge for joint 16, one base cartridge (which includes acounter balance) for short joint 18 and two hinge cartridges for joints32 and 36. In addition, as is consistent with the taper of articulatedarm 14, the cartridges nearest the base (e.g., located in long joint 16and short joint 18) have a larger diameter relative to the smallerdiameters of joints 30, 32, 34 and 36. Each cartridge includes apre-loaded bearing arrangement and a transducer which in thisembodiment, comprises a digital encoder. Turning to FIGS. 9 and 10, thecartridge 44 positioned in axial long joint 16 will now be described.

[0089] Cartridge 44 includes a pair of bearings 50, 52 separated by aninner sleeve 54 and outer sleeve 56. It is important that bearings 50,52 are pre-loaded. In this embodiment, such preload is provided bysleeves 54, 56 being of differing lengths (inner sleeve 54 is shorterthan outer sleeve 56 by approximately 0.0005 inch) so that upontightening, a preslected preload is generated on bearings 50, 52.Bearings 50, 52 are sealed using seals 58 with this assembly beingrotatably mounted on shaft 60. At its upper surface, shaft 60 terminatesat a shaft upper housing 62. An annulus 63 is defined between shaft 60and shaft upper housing 62. This entire assembly is positioned withinouter cartridge housing 64 with the shaft and its bearing assembly beingsecurely attached to housing 64 using a combination of an inner nut 66and an outer nut 68. Note that upon assembly, the upper portion 65 ofouter housing 64 will be received within annulus 63. It will beappreciated that the aforementioned preload is provided to bearings 50,52 upon the tightening of the inner and outer nuts 66, 68 which providecompression forces to the bearings and, because of the difference inlength between the inner and outer spacers 54, 56, the desired preloadwill be applied.

[0090] Preferably, bearings 50, 52 are duplex ball bearings. In order toobtain the adequate pre-loading, it is important that the bearing facesbe as parallel as possible. The parallelism affects the evenness of thepre-loading about the circumference of the bearing. Uneven loading willgive the bearing a rough uneven running torque feel and will result inunpredictable radial run out and reduced encoder performance. Radial runout of the modularly mounted encoder disk (to be discussed below) willresult in an undesirable fringe pattern shift beneath the reader head.This results in significant encoder angular measurement errors.Furthermore, the stiffness of the preferably duplex bearing structure isdirectly related to the separation of the bearings. The farther apartthe bearings, the stiffer will be the assembly. The spacers 54, 56 areused to enhance the separation of the bearings. Since the cartridgehousing 64 is preferably aluminum, then the spacers 54, 56 will alsopreferably be made from aluminum and precision machined in length andparallelism. As a result, changes in temperature will not result indifferential expansion which would compromise the preload. As mentioned,the preload is established by designing in a known difference in thelength of spacers 54, 56. Once the nuts 66, 68 are fully tightened, thisdifferential in length will result in a bearing preload. The use ofseals 58 provide sealed bearings since any contamination thereof wouldeffect all rotational movement and encoder accuracy, as well as jointfeel.

[0091] While cartridge 44 preferably includes a pair of spaced bearings,cartridge 44 could alternatively include a single bearing or three ormore bearings. Thus, each cartridge needs at least one bearing as aminimum.

[0092] The joint cartridges of the present invention may either haveunlimited rotation or as an alternative, may have a limited rotation.For a limited rotation, a groove 70 on a flange 72 on the outer surfaceof housing 64 provides a cylindrical track which receives a shuttle 74.Shuttle 74 will ride within track 70 until it abuts a removable shuttlestop such as the rotation stop set screws 76 whereupon rotation will beprecluded. The amount of rotation can vary depending on what is desired.In a preferred embodiment, shuttle rotation would be limited to lessthan 720°. Rotational shuttle stops of the type herein are described inmore detail in commonly owned U.S. Pat. No. 5,611,147, all of thecontents of which have been incorporated herein by reference.

[0093] As mentioned, in an alternative embodiment, the joint used in thepresent invention may have unlimited rotation. In this latter case, aknown slip ring assembly is used. Preferably, shaft 60 has a hollow oraxial opening 78 therethrough which has a larger diameter section 80 atone end thereof. Abutting the shoulder defined at the intersectionbetween axial openings 78 and 80 is a cylindrical slip ring assembly 82.Slip ring assembly 82 is non-structural (that is, provides no mechanicalfunction but only provides an electrical and/or signal transferfunction) with respect to the preloaded bearing assembly set forth inthe modular joint cartridge. While slip ring assembly 82 may consist ofany commercially available slip ring, in a preferred embodiment, slipring assembly 82 comprises a H series slip ring available from IDMElectronics Ltd. of Reading, Berkshire, United Kingdom. Such slip ringsare compact in size and with their cylindrical design, are ideallysuited for use in the opening 80 within shaft 60. Axial opening 80through shaft 60 terminates at an aperture 84 which communicates with achannel 86 sized and configured to receive wiring from the slip ringassembly 82. Such wiring is secured in place and protected by a wirecover 88 which snaps onto and is received into channel 86 and aperture84. Such wiring is shown diagrammatically at 90 in FIG. 10.

[0094] As mentioned, modular cartridge 44 include both a preloadedbearing structure which has been described above as well as a modularencoder structure which will now be described. Still referring to FIGS.9 and 10, the preferred transducer used in the present inventioncomprises a modular optical encoder having two primary components, aread head 92 and a grating disk 94. In this embodiment, a pair of readheads 92 are positioned on a read head connector board 96. Connectorboard 96 is attached (via fasteners 98) to a mounting plate 100. Disk 94is preferably attached to the lower bearing surface 102 of shaft 60(preferably using a suitable adhesive) and will be spaced from and inalignment with read heads 92 (which is supported and held by plate 100).A wire funnel 104 and sealing cap 106 provide the final outer coveringto the lower end of housing 64. Wire funnel 104 will capture and retainwiring 90 as best shown in FIG. 10. It will be appreciated that theencoder disk 94 will be retained by and rotate with shaft 60 due to theapplication of adhesive at 102. FIGS. 9 and 10 depict a double read head92; however, it will be appreciated that more than two read heads may beused or, in the alternative, a single read head as shown in FIG. 9A maybe used. FIGS. 9B-E depict examples of modular cartridges 44 with morethan two read heads. FIGS. 9B-C show four read heads 92 received in aplate 100 and spaced at 90 degree intervals (although different relativespacings may be appropriate). FIGS. 9D-E show three read heads 92received in a plate 100 and spaced at 120 degree intervals (althoughdifferent relative spacing may be appropriate).

[0095] In order to properly align disk 94, a hole (not shown) isprovided through housing 64 at a location adjacent disk 94. A tool (notshown) is then used to push disk 94 into proper alignment whereuponadhesive between disk 94 and shaft 66 is cured to lock disk 94 in place.A hole plug 73 is then provided through the hole in housing 64.

[0096] It is important to note that the locations of disk 94 and readhead 92 may be reversed whereby disk 94 is attached to housing 56 andread head 92 rotates with shaft 60. Such an embodiment is shown in FIG.12A where board 96′ is attached (via adhesive) to shaft 60′ for rotationtherewith. A pair of read heads 92′ are attached to board 96′ and thuswill rotate with shaft 60′. The disk 94′ is positioned on a support 100′which is attached to housing 64′. In any event, it will be appreciatedthat either the disk 94 or read head 92 may be mounted for rotation withthe shaft. All that is important is that disk 94 and read head 92 bepositioned in a cartridge (or joint) so as to be rotatable with respectto each other while maintaining optical communication.

[0097] Preferably, the rotational encoder employed in the presentinvention is similar to that disclosed in U.S. Pat. Nos. 5,486,923 and5,559,600, all of the contents of which are incorporated herein byreference. Such modular encoders are commercially available from MicroESystems under the trade name Pure Precision Optics. These encoders arebased on physical optics that detect the interference betweendiffraction orders to produce nearly perfect sinusoidal signals from aphoto detector array (e.g., read head(s)) inserted in the fringepattern. The sinusoidal signals are electronically interpolated to allowdetection of displacement that is only a fraction of the optical fringe.

[0098] Using a laser light source, the laser beam is first collimated bya lens and then sized by an aperture. The collimated size beam passesthrough a grating that diffracts the light into discrete orders with the0^(th) and all even orders suppressed by the grating construction. Withthe 0 order suppressed, a region exists beyond the diverging 3^(rd)order where only the ±1^(st) orders overlap to create a nearly puresinusoidal interference. One or more photodetector arrays (read heads)are placed within this region, and produces four channels of nearly puresinusoidal output when there is relative motion between the grating andthe detector. Electronics amplify, normalize and interpolate the outputto the desired level of resolution.

[0099] The simplicity of this encoder design yields several advantagesover prior art optical encoders. Measurements may be made with only alaser source and its collimating optics, a diffractive grating, and adetector array. This results in an extremely compact encoder systemrelative to the bulkier prior art, conventional encoders. In addition, adirect relationship between the grating and the fringe movementdesensitizes the encoder from environmentally induced errors to whichprior art devices are susceptible. Furthermore, because the region ofinterference is large, and because nearly sinusoidal interference isobtained everywhere within this region, alignment tolerances are farmore relaxed than is associated with prior art encoders.

[0100] A significant advantage of the aforementioned optical encoder isthat the precision of the standoff orientation and distance or thedistance and orientation of the read head with respect to the encoderdisk is far less stringent. This permits a high accuracy rotationalmeasurement and an easy-to-assemble package. The result of using this“geometry tolerant” encoder technology results in a CMM 10 havingsignificant cost reductions and ease of manufacturing.

[0101] It will be appreciated that while the preferred embodimentdescribed above includes an optical disk 94, the preferred embodiment ofthe present invention also encompasses any optical fringe pattern whichallow the read head to measure relative motion. As used herein, suchfringe pattern means any periodic array of optical elements whichprovide for the measurement of motion. Such optical elements or fringepattern could be mounted on a rotating or stationary disk as describedabove, or alternatively, could be deposited, secured or otherwisepositioned or reside upon any of the relatively moving components (suchas the shaft, bearings or housing) of the cartridge.

[0102] Indeed, the read head and associated periodic array or patterndoes not necessarily need to be based on optics (as described above) atall. Rather, in a broader sense, the read head could read (or sense)some other periodic pattern of some other measurable quantity orcharacteristic which can be used to measure motion, generally rotarymotion. Such other measurable characteristics may include, for example,reflectivity, opacity, magnetic field, capacitance, inductance orsurface roughness. (Note that a surface roughness pattern could be readusing a read head or sensor in the form of a camera such as a CCDcamera). In such cases, the read head would measure, for example,periodic changes in magnetic field, reflectivity, capacitance,inductance, surface roughness or the like. As used herein therefore, theterm “read head” means any sensor or transducer and associatedelectronics for analysis of these measurable quantities orcharacteristics with an optical read head being just one preferredexample. Of course, the periodic pattern being read by the read head canreside on any surface so long as there is relative (generally rotary)motion between the read head and periodic pattern. Examples of theperiodic pattern include a magnetic, inductive or capacitive mediadeposited on a rotary or stationary component in a pattern. Moreover, ifsurface roughness is the periodic pattern to be read, there is no needto deposit or otherwise provide a separate periodic media since thesurface roughness of any component in communication with the associatedread head (probably a camera such as a CCD camera) may be used.

[0103] As mentioned, FIGS. 9 and 10 depict the elements of the modularbearing and encoder cartridge for axially long joint 16. FIGS. 11 and 12depict the bearing and encoder cartridge for axial long joints 30 and34. These cartridge assemblies are substantially similar to that shownFIGS. 9 and 10 and so are designated by 44′. Minor differences areevident from the FIGURES relative to cartridge 44 with respect to, forexample, a differently configured wire cap/cover 88′, slightly differingwire funnels/covers 104′, 106′ and the positioning of flange 72′ at theupper end of housing 64′. Also, the flanges between housing 64′ andshaft upper housing 62 are flared outwardly. Of course, the relativelengths of the various components shown in FIGS. 11 and 12 may differslightly from that shown in FIGS. 9 and 10. Since all of thesecomponents are substantially similar, the components have been given thesame identification numeral with the addition of a prime. FIG. 11A issimilar to FIG. 11, but depicts a single read head embodiment.

[0104] Turning to FIGS. 13 and 14, similar exploded and cross-sectionalviews are shown for the bearing and encoder cartridges in short hingejoints 32 and 36. As in the long axial joints 44′ of FIGS. 11 and 12,the cartridges for the short hinge joints 32 and 36 are substantiallysimilar to the cartridge 44 discussed in detail above and therefore thecomponents of these cartridges are identified at 44″ with similarcomponents being identified using a double prime. It will be appreciatedthat because cartridges 44″ are intended for use in short joints 32, 36,no slip ring assembly is required as the wiring will simply pass throughthe axial openings 78″, 80″ due to the hinged motion of these joints.FIG. 13A is similar to FIG. 13, but depicts a single read headembodiment.

[0105] Finally, with reference to FIGS. 15 and 16, the modularbearing/encoder cartridge for short hinge joint 18 is shown at 108. Itwill be appreciated that substantially all of the components ofcartridge 108 are similar or the same as the components in cartridges44, 44′ and 44″ with the important exception being the inclusion of acounter balance assembly. This counter balance assembly includes acounter balance spring 110 which is received over housing 64″ andprovides an important counter balance function to CMM IO in a mannerwhich will be described hereinafter with reference to FIGS. 26 to 28.FIG. 15A is similar to FIG. 15, but depicts a single read headembodiment.

[0106] As mentioned, in a preferred embodiment, more than one read headmay be used in the encoder. It will be appreciated that anglemeasurement of an encoder is effected by disk run out or radial motiondue to applied loads. It has been determined that two read headspositioned at 180° from each other will result in run out causingcancellation effects in each read head. These cancellation effects areaveraged for a final “immune” angle measurement. Thus, the use of tworead heads and the resultant error cancellation will result in a lesserror prone and more accurate encoder measurement. FIGS. 17-19 depictthe bottom, cross-sectional and top views respectively for a dual readhead embodiment useful in, for example, a larger diameter cartridge suchas found in joints 16 and 18 (that is, those joints nearest the base).Thus, a cartridge end cap 100 has mounted thereto a pair of circuitboards 96 with each circuit board 96 having a read head 92 mechanicallyattached thereto. The read heads 92 are preferably positioned 180° apartfrom each other to provide for the error cancellation resulting from therun out or radial motion of the disk. Each board 96 additionallyincludes a connector 93 for attachment of the circuit board 96 to theinternal bus and/or other wiring as will be discussed hereinafter. FIGS.20-22 depict substantially the same components as in FIGS. 17-19 withthe primary difference being a smaller diameter cartridge end cap 100.This smaller diameter dual read head embodiment would be associated withthe smaller diameter cartridges of, for example, joints 30, 32, 34 and36.

[0107] The use of at least two read heads (or more such as the threereads heads shown in FIGS. 9D-E and the four read heads shown in FIGS.9B-C) is also advantageously employed in more conventional coordinatemeasurement machines to significantly reduce the cost and complexity ofmanufacture thereof. For example, a coordinate measurement machinedescribed in U.S. Pat. No. 5,794,356 (hereinafter “Raab '356”),incorporated herein by reference, includes a relatively simpleconstruction for each joint including a first housing that remainsstationary with one joint half, and a second housing that remainsstationary with the second joint half, the first and second housingshaving pre-loaded bearings that allow them to rotate with each other.The first housing retains a packaged encoder and the second housingincludes an axially-disposed internal shaft that extends into the firsthousing and mates with the encoder shaft protruding from the packagedencoder. The prior art packaged encoder required that there be no loadsapplied thereto and that the motion of the second housing be accuratelytransmitted to the encoder despite small misalignments of the axis ofthe internal shaft and the axis of the packaged encoder to maintain thehighly accurate rotational measurements. To accommodate manufacturingtolerances in axial misalignment, a special coupling device is connectedbetween the encoder shaft and the internal shaft. Such a structure canbe seen in FIG. 7 of Raab '356.

[0108] In contrast, FIG. 35 shows a modified structure in which thecoupling device and packaged encoder from the Raab '356 CMM are removedand replaced with encoder disk 96 and end cap 100. Here, two joints arepositioned at 90° to each other, each joint having a first housing 420and a second housing 410. Internal shaft 412 extends from second housing420 into first housing 410. As shown, encoder disk 96 is attached, e.g.,using adhesive, to the end of internal shaft 412 while end cap 100 isfixed within first housing 420. However, it will be understood thatencoder disk 96 may be fixed within first housing 420 and end cap 100 befixed to internal shaft 412 without affecting the operation of thejoint.

[0109] As previously described, the use of two (or more) read heads andthe resultant error cancellation will result in a less error prone andmore accurate encoder measurement despite small axial misalignments. Inaddition, a direct relationship between the grating and the fringemovement desensitizes the encoder from environmentally induced errors towhich prior art devices are susceptible. Furthermore, because the regionof interference is large, and because nearly sinusoidal interference isobtained everywhere within this region, alignment tolerances are farmore relaxed than is associated with prior art encoders as previouslydescribed.

[0110] In another example, U.S. Pat. No. 5,829,148 to Eaton (hereinafter“Eaton '148”), incorporated herein by reference, describes a prior artCMM in which a packaged encoder forms an integral part of each joint byproviding primary rotational bearings, therefore avoiding any need tocompensate for axial misalignments as required in Raab '356 discussedabove. However, because the encoder provides primary rotationalbearings, it is important that the encoder be structurally rugged andable to be subjected to various loadings without affecting itsperformance. This adds to the cost and bulkiness of the encoder. Such astructure can be seen in FIG. 4 of Eaton '148.

[0111] In contrast, FIG. 36 shows a modified structure in which thepackaged encoder and connecting shaft of one joint from the Eaton '148CMM is removed and replaced by end cap 100 and encoder disk 96. Here afirst housing 470 retains end cap 100 and retains internal shaft 462 ofsecond housing 460 by bearings 472. Internal shaft 462 is extended toterminate proximate end cap 100 and encoder disk 96 is attached, e.g.,using adhesive, at the end of internal shaft 462. As in the embodimentshown in FIG. 35, the use of two (or more) read heads significantlyreduces the cost and complexity of the joint without sacrificingaccuracy.

[0112] It will be appreciated that non-circularity of the motion of theperiodic pattern is the primary cause for inaccuracies in a rotationaltransducer of the types described herein. This non-circularity of motioncan be due to a number of phenomena including assembly imperfections andexternal deformations. External deformations can occur anywhere in theCMM and most generally occur with respect to the bearing structureand/or the joint tubing. For example, such external deformation canresult from non-repeatable bearing run-out, bearing wobble, bearingdeformation, thermal affects and bearing play. As discussed with respectto FIGS. 17-21, in one embodiment of this invention, the inaccuracies ofthe rotational transducers are corrected for using at least two readheads, preferably mounted at 180° apart from each other. However, instill another embodiment of this invention shown in FIGS. 41-43, thepossible error derived from deformations to the CMM and/or assemblyimperfections are corrected using a combination of at least one readhead with one or more sensors, preferably a plurality of proximitysensors (or any other sensor which measures displacement).

[0113] It will be appreciated that in any given cartridge of the typedescribed herein, there are six degrees of freedom between the shaft andthe housing of the cartridge. That is, the shaft includes six degrees offreedom, namely X, Y and Z axis displacement and X, Y, and Z axisrotation. Turning now to FIGS. 41-43, a cartridge of the type describedabove is shown at 600. Cartridge 600 includes an internal shaft 602rotationally mounted on bearings (not shown) within a housing 606. Readhead plate 604 secures an encoder read head 610 and sensors S1-S5 tohousing 606. An encoder disk 608 having an optical fringe patternthereon is attached to shaft 602 for rotation therewith. Encoder readhead 610 (attached to read head plate 604) is mounted above opticalfringe pattern 608 and preferably functions to measure Z axis rotationof shaft 602. In addition to read head 610, cartridge 600 includes fiveadditional sensors, all of which are fixed to housing 606 through readhead plate 604; and all of which are intended to measure relativemovement between the shaft 602 and housing 606. These additional sensorsinclude a displacement sensor S1 for measuring Y axis displacement ofshaft 602 (with respect to housing 606) and a displacement sensor S2 formeasuring X axis displacement of shaft 602 (with respect to housing606). Thus, shaft 602 has associated with it three sensors, namely readhead 610 and sensors S1 and S2 for respectively measuring the Z axisrotation and the X and Y axis displacement thereof. Preferably, theshaft 602 includes three additional sensors associated with it formeasuring X and Y axis rotation and Z axis displacement. Specifically,sensors S3, S4 and S5 in combination measure the X and Y axis ofrotation as well as the Z axis displacement. In the embodiment shown inFIGS. 41-43, the S3, S4 and S5 sensors are spaced along the read headplate 604 at 120° intervals. The measurements from these equidistantlyspaced three sensors are combined in a known manner to determine thecombined X and Y axis rotation and Z axis displacement.

[0114] Thus, these additional five sensors S1-S5 measure and correct forany deformations in the CMM including the joint tubes or the bearingstructure and these sensors can be used to correct for such error inmeasurement. These additional sensors are therefore used to measurerelative motions between the shaft and housing to determine movementsother than the rotary movement of the disk and therefore correct for anyerrors caused by these “other” movements. Any suitable type of sensorfor carrying out these displacement measurements may be used inaccordance with the present invention. Preferably the sensors areproximity sensors such as proximity sensors using Hall effects, orproximity sensors based on magneto, resistive, capacitive or opticalcharacteristics.

[0115] It will be appreciated that, when for example, a joint is placedunder load and the bearing structure deforms (and as a result of suchdeformation, the shaft 602 carrying the optical pattern 608 and thehousing 606 with the read head 610 will move with respect to eachother), the angular measurement which will be affected by such movementwill be “corrected” using the displacement information from theadditional sensors S1-S5 (it being appreciated that the presentinvention contemplates the use of all or less than all of the sensorsS1-S5 and moreover further contemplates the use of sensors in additionto S1 through S5). This correction results in substantially improvedaccuracy for the portable CMM. It will further be appreciated that whilethe invention contemplates at least one of the joint cartridgesincluding additional sensors S1-S5, in a preferred embodiment, all ofthe cartridges would include such additional sensors. Also, while theFIGS. 41-43 embodiment is shown with a rotary encoder having an opticalgrating disk, any of the alternative rotary encoders describedpreviously which detect and analyze a periodic pattern of a measurablecharacteristic including those employing measurable characteristics sucha reflectivity, opacity, magnetic field, capacitance, inductance orsurface roughness, may be utilized with the sensors S1-S5 as describedherein. Also, while the FIGS. 41-43 embodiment depict an embodimentwherein the optical disk rotates with the shaft 602, the multiplesensors S1-S5 may also be used with an embodiment such as that shown inFIG. 12A where the optical disk is stationary.

[0116] While, as discussed above, the additional sensors could be usedto correct for errors caused by bearing and other arm deformations, theadditional sensors may also be used to calculate and measure theexternal forces directed at the joint which are actually causing suchstructural deformation. These measurements may be advantageouslyutilized so as to provide sensory feedback to the user. For example,certain ranges of external forces can be tolerated on a particularbearing structure or joint; however, the sensing of external forces bydeformation of the bearing arrangement can be used to indicate thatthese ranges have been exceeded and thereafter provide sensory feedbackto the user so as to take remedial action to alleviate such externalforces. That is, the user can then modify the handling of the CMM inorder to improve the measurement. This sensory feedback may be in theform of auditory and/or visual feedback; and may be indicated bysoftware controlling the CMM. Thus, the additional sensors S1-S5described above can act as overload sensors and prevent the user fromoverstressing the arm and thereby maintain optimum precision so as toinsure precise measurement. Indeed, the measurement of the externalforce on a given joint may be utilized not only with the embodiment ofFIGS. 41-43 (wherein additional sensors S1-S5 are employed) but alsowith the above-discussed embodiments wherein two or more read heads areemployed. In the case of the two read head arrangement, the angularmeasurement is derived from the average of the two read heads. The forceof deformation can then be obtained by measuring the difference betweenthe two read head readings. In the case of the FIGS. 41-43 embodiments,the deformation can be measured in the direction of each of the twoproximity sensors. This provides additional directional information.Using all six sensors (S1-S5 and the read head) will provide a totaldescription of the deformations in each of the joints due to themeasurement of all six degrees of freedom.

[0117] In addition to the improvements in the angular accuracy of thetransducer provided by either the use of two read heads or the use of asingle read head together with one or more proximity sensors, theinformation derived from measuring the force of deformation can also beused to correct the kinematics of the arm by using such deformationinformation to change the dimension of the arm in real time and therebyimprove the accuracy of the measurement. Thus, for example, if thebearings are deformed, this deformation will cause a change in thelength of a segment of the arm. By measuring this deformation using thesensors and read heads as described herein, this change in the length ofthe arm can be taken into account in the measurement software associatedwith the CMM and then used as a correction to improve the ultimatemeasurement accuracy of the arm.

[0118] Turning now to FIG. 23A, a block diagram of the electronics isshown for the single read head embodiment of FIGS. 9A, 11A, 13A and 15A.It will be appreciated that CMM 10 preferably includes an external bus(preferably a USB bus) 260 and an internal bus (preferably RS-485) 261which is designed to be expandable for more encoders as well as eitheran externally mounted rail or additional rotational axes such as aseventh axis. The internal bus is preferably consistent with RS485 andthis bus is preferably configured to be used as a serial network in amanner consistent with the serial network for communicating data fromtransducers in a portable CMM arm as disclosed in commonly assigned U.S.Pat. No. 6,219,928, all of the contents of which have been incorporatedherein by reference.

[0119] With reference to FIG. 23A, it will be appreciated that eachencoder in each cartridge is associated with an encoder board. Theencoder board for the cartridge in joint 16 is positioned within base 12and is identified at 112 in FIG. 25. The encoders for joints 18 and 30are processed on a dual encoder board which is located in the secondlong joint 30 and is identified at 114 in FIG. 26. FIG. 26 also depictsa similar dual encoder board 116 for the encoders used in joints 32 and34, board 116 being positioned in third long joint 34 as shown in FIG.26. Finally, the end encoder board 118 is positioned within measurementprobe handle 28 as shown in FIG. 24 and is used to process the encodersin short joint 36. Each of the boards 114, 116 and 118 are associatedwith a thermocouple to provide for thermal compensation due totemperature transients. Each board 112, 114, 116 and 118 incorporatesembedded analog-to-digital conversion, encoder counting and serial portcommunications. Each board also has read programmable flash memory toallow local storage of operating data. The main processor board 112 isalso field programmable through the external USB bus 260. As mentioned,the internal bus (RS-485) 261 is designed to be expandable for moreencoders which also includes either an externally mounted rail and/orseventh rotation axis. An axis port has been provided to provideinternal bus diagnosis. Multiple CMMs of the type depicted at 10 inthese FIGURES may be attached to a single application due to thecapabilities of the external USB communications protocol. Moreover,multiple applications may be attached to a single CMM 10 for the verysame reasons.

[0120] Preferably, each board 112, 114, 116 and 118 includes a 16-bitdigital signal processor such as the processor available from Motorolaunder the designation DSP56F807. This single processing componentcombines many processing features including serial communication,quadrature decoding, A/D converters and on-board memory thus allowing areduction of the total number of chips needed for each board.

[0121] In accordance with another important feature of the presentinvention, each of the encoders is associated with an individualizedidentification chip 120. This chip will identify each individual encoderand therefore will identify each individual bearing/encoder modularcartridge so as to ease and expedite quality control, testing, andrepair.

[0122]FIG. 23B is an electronics block diagram which is similar to FIG.23A, but depicts the dual read head embodiment of FIGS. 10, 12, 14 and16-22.

[0123] With reference to FIGS. 24-26, the assembly of each cartridge inthe articulated arm 14 will now be described (note that FIG. 24 depictsarm 10 without base 12. Note also that FIGS. 24-26 employ the singleread head embodiments of FIGS. 9A, 11A, 13A and 15A). As shown in FIG.25, the first long joint 16 includes a relatively long cartridge 44, theupper end of which has been inserted into a cylindrical socket 120 ofdual socket joint 46. Cartridge 44 is securely retained within socket120 using a suitable adhesive. The opposite, lower end of cartridge 44is inserted into an extension tube, which in this embodiment may be analuminum sleeve 122 (but sleeve 122 may also be comprised of a stiffalloy or composite material). Cartridge 44 is secured in sleeve 122again using a suitable adhesive. The lower end of sleeve 122 includes alarger outer diameter section 124 having internal threading 126 thereon.Such threading is outwardly tapered and is configured to threadably matewith inwardly tapered threading 128 on magnetic mount housing 130 as isclearly shown in FIG. 4. As has been discussed, all of the severaljoints of CMM 10 are interconnected using such tapered threading.Preferably, the tapered thread is of the NPT type which isself-tightening and therefore no lock nuts or other fastening devicesare needed. This threading also allows for and should include a threadlocking agent.

[0124] Turning to FIG. 26, as in first long joint 16, long cartridge 44′is adhesively secured in the cylindrical opening 120′ of dual socketjoint 46′. The outer housing 64′ of cartridge 44′ includes a shoulder132 defined by the lower surface of flange 72′. This shoulder 132supports cylindrical extension tube 134 which is provided over andsurrounds the outer surface of housing 64′. Extension tubes are used inthe joints to create a variable length tube for attachment to a threadedcomponent. Extension tube 134 thus extends outwardly from the bottom ofcartridge 64′ and has inserted therein a threaded sleeve 136.Appropriate adhesive is used to bond housing 44′ to extension tube 134as well as to bond sleeve 136 and tube 134 together. Sleeve 136terminates at a tapered section having outer threading 138 thereon.Outer threading threadably mates with internal threading 140 onconnecting piece 142 which has been adhesively secured in opening 144 ofdual socket joint 48. Preferably, extension tube 134 is composed of acomposite material such as an appropriate carbon fiber composite whilethreadable sleeve 136 is composed of aluminum so as to match the thermalproperties of the dual socket joint 48. It will be appreciated that PCboard 114 is fastened to a support 146 which in turn is secured to dualsocket joint support 142.

[0125] In addition to the aforementioned threaded connections, one, someor all of the joints may be interconnected using threaded fasteners asshown in FIGS. 25A-B. Rather than the threaded sleeve 136 of FIG. 26,sleeve 136′ of FIG. 25B has a smooth tapered end 137 which is receivedin a complimentary tapered socket support 142′. A flange 139 extendscircumferentially outwardly from sleeve 136′ with an array of bolt holes(in this case 6) therethrough for receiving threaded bolts 141. Bolts141 are threadably received in corresponding holes along the uppersurface of socket support 142′. An extension tube 134′ is received oversleeve 136′ as in the FIG. 26 embodiment. The complimentary tapered maleand female interconnections for the joints provide improved connectioninterfaces relative to the prior art.

[0126] Still referring to FIG. 26, long cartridge 44″ of third longjoint 34 is secured to arm 14 in a manner similar to cartridge 44′ oflong joint 30. That is, the upper portion of cartridge 44″ is adhesivelysecured into an opening 120″ of dual socket joint 46″. An extension tube148 (preferably composed of a composite material as described withrespect to tube 134) is positioned over outer housing 64″ and extendsoutwardly thereof so as to receive a mating sleeve 150 which isadhesively secured to the interior diameter of extension tube 148.Mating sleeve 150 terminates at a tapered section having outer threading152 and mates with complimentary interior threading 153 on dual socketjoint support 154 which has been adhesively attached to a cylindricalsocket 156 within dual socket joint 148′. Printed circuit board 116 issimilarly connected to the dual socket joint using the PCB support 146′which is secured to dual socket joint support 154.

[0127] As discussed with respect to FIGS. 7 and 8, the short cartridges44′ in FIGS. 13 and 14 and 108 of FIG. 15 are simply positioned betweentwo dual socket joints 46, 48 and are secured within the dual socketjoints using an appropriate adhesive. As a result, the long and shortcartridges are easily attached to each other at right angles (or, ifdesired, at angles other than right angles).

[0128] The modular bearing/transducer cartridges as described aboveconstitute an important technological advance in portable CMMs such asshown, for example, in the aforementioned Raab '356 and Eaton '148patents. This is because the cartridge (or housing of the cartridge)actually defines a structural element of each joint which makes up thearticulated arm. As used herein, “structural element” means that thesurface of the cartridge (e.g., the cartridge housing) is rigidlyattached to the other structural components of the articulated arm inorder to transfer rotation without deformation of the arm (or at most,with only de minimis deformation). This is in contrast to conventionalportable CMMs (such as disclosed in the Raab '356 and Eaton '148patents) wherein separate and distinct joint elements and transferelements are required with the rotary encoders being part of the jointelements (but not the transfer elements). In essence, the presentinvention has eliminated the need for separate transfer elements (e.g.,transfer members) by combining the functionality of the joint andtransfer elements into a singular modular component (i.e., cartridge).Hence, rather than an articulated arm comprised of separate and distinctjoints and transfer members, the present invention utilizes anarticulated arm made up of a combination of longer and shorter jointelements (i.e., cartridges), all of which are structural elements of thearm. This leads to better efficiencies relative to the prior art. Forexample, the number of bearings used in a joint/transfer membercombination in the '148 and '582 patent was four (two bearings in thejoint and two bearings in the transfer member) whereas the modularbearing/transducer cartridge of the present invention may utilize aminimum of one bearing (although two bearings are preferred) and stillaccomplish the same functionality (although in a different and improvedway).

[0129] FIGS. 24A and 26A-B are cross-sectional views, similar to FIGS.24-26, but showing the dual read head embodiments of FIGS. 10, 12, 14and 16-22 and are further cross-sections of the CMM 10′ shown in FIG.3A.

[0130] The overall length of articulated arm 14 and/or the various armsegments may vary depending on its intended application. In oneembodiment, the articulated arm may have an overall length of about 24inches and provide measurements on the order of about 0.0002 inch to0.0005 inch. This arm dimension and measurement accuracy provides aportable CMM which is well suited for measurements now accomplishedusing typical hand tools such as micrometers, height gages, calipers andthe like. Of course, articulated arm 14 could have smaller or largerdimensions and accuracy levels. For example, larger arms may have anoverall length of 8 or 12 feet and associated measurement accuracies of0.001 inch thus allowing for use in most real time inspectionapplications or for use in reverse engineering.

[0131] CMM 10 may also be used with a controller mounted thereto andused to run a relatively simplified executable program as disclosed inaforementioned U.S. Pat. No. 5,978,748 and application Ser. No.09/775,226; or may be used with more complex programs on host computer172.

[0132] With reference to FIGS. 1-6 and 24-26, in a preferred embodiment,each of the long and short joints are protected by an elastomeric bumperor cover which acts to limit high impact shock and provide ergonomicallypleasant gripping locations (as well as an aesthetically pleasingappearance). The long joints 16, 30 and 34 are all protected by a rigidplastic (e.g., ABS) replaceable cover which serves as an impact andabrasion protector. For the first long joint 16, this rigid plasticreplaceable cover comes in the form of the two-piece base housing 26Aand 26B as is also shown in FIG. 4. Long joints 30 and 34 are eachprotected by a pair of cover pieces 40 and 41 which, as shown in FIGS. 5and 6 may be fastened together in a clam shell fashion using appropriatescrews so as to form a protective sleeve. It will be appreciated that ina preferred embodiment, this rigid plastic replaceable cover for eachlong joint 30 and 34 will surround the preferably composite (carbonfiber) extension tube 134 and 148, respectively.

[0133] Preferably, one of the covers, in this case cover section 41,includes a slanted support post 166 integrally molded therein whichlimits the rotation at the elbow of the arm so as to restrict probe 28from colliding with base 12 in the rest position. This is best shown inFIGS. 3, 24 and 26. It will be appreciated that post 166 will thus limitunnecessary impact and abrasion.

[0134] As will be discussed with respect to FIGS. 29 and 31, probe 28may also include a replaceable plastic protective cover made from arigid plastic material.

[0135]FIGS. 3A, 24A and 26A-B depict alternative protective sleeves 40′,41′ which also have a clam shell construction, but are held in placeusing straps or spring clips 167 rather than threaded fasteners.

[0136] Each of the short joints 18, 32 and 36 include a pair ofelastomeric (e.g., thermoplastic rubber such as Santoprene®) bumpers 38as previously mentioned and as shown clearly in FIGS. 1-3 and 5-6.Bumpers 38 may either be attached using a threaded fastener, a suitableadhesive or in any other suitable manner. Elastomeric or rubber bumper38 will limit the high impact shock as well as provide an aestheticallypleasing and ergonomically pleasant gripping location.

[0137] The foregoing covers 40, 41, 40′, 41′ and bumpers 38 are alleasily replaceable (as is the base housing 26A, 26B) and allow arm 14 toquickly and inexpensively be refurbished without influencing themechanical performance of CMM 10.

[0138] Still referring to FIGS. 1-3, base-housing 26A, B includes atleast two cylindrical bosses for the mounting of a sphere as shown at168 in FIG. 3. The sphere may be used for the mounting of a clamp typecomputer holder 170 which in turn supports a portable or other computerdevice 172 (e.g., the “host computer”). Preferably, a cylindrical bossis provided on either side of base housing 26A, B so that the ball andclamp computer mount may be mounted on either side of CMM 10.

[0139] Turning now to FIGS. 15, 16, 27A, B and 28, the preferred counterbalance for use with CMM 10 will now be described. Conventionally,portable CMMs of the type described herein have utilized an externallymounted coil spring which has been mounted separately in outriggerfashion on the outside of the articulated arm for use as a counterbalance. In contrast, the present invention utilizes a fully integratedinternal counter balance which leads to a lower overall profile for thearticulated arm. Typically, prior art counter balances have utilizedwound coil springs in the counter balance mechanism. However, inaccordance with an important feature of the present invention, thecounter balance employs a machined coil spring (as opposed to a woundcoil spring). This machined spring 110 is shown in FIGS. 16 and 27A-Band is formed from a single cylinder of metal (steel) which is machinedto provide a pair of relatively wide rings 174, 176 at opposed ends ofthe coil and relatively narrower rings 178 forming the intermediatecoils between end coils 174, 176. It will be appreciated that the widerend rings 174, 176 engage with the respective side surfaces 180 of shaft62′ and 182 of housing 64″ thereby preventing lateral movement of spring110. The wider, solid end rings 174, 176 act as an anti-twist device andprovide superior function relative to prior art wound springs. End ring174 preferably includes a pair of locking posts 184, 186 (although onlyone locking post may be employed) while end ring 176 includes a lockingpost 188.

[0140] With reference to FIG. 27B, each dual socket joint 46, 48includes channels such as shown at 190 and 191 in dual socket joint 46for receiving a respective post 184, 186 or 188. With reference to FIG.28, while pins 184, 186 will remain in a fixed position within theappropriate channel or groove of dual socket joint 48, the location ofpin 188 may be changed so as to optimize the overall wind-up on spring110 and provide the most efficient counter balance force. This isaccomplished using a threaded hole 192 which receives threaded screw194. As shown in FIG. 28, screw 194 may be operated on to contact pin188 and move pin 188 circumferentially in a clock-wise direction alonginterior channel 196 which is shown in FIG. 27B as being perpendicularto pin access groove 190. Screw 194 is preferably positioned to optimizespring 110 in the factory.

[0141] It will be appreciated that during use of articulated arm 14, theencoder/bearing cartridge 108 will act as a hinge joint and onceinserted and adhesively secured within the sockets of dual socket joints46, 48, pins 184, 186 and 188 will be locked in their respectivegrooves. When socket joint 48 is rotated relative to socket joint 46(via the hinge joint of cartridge 108), spring 110 will wind-up. When itis desired that socket joint 48 rotate back to its original position,the wound forces of spring 110 will unwind providing the desired counterbalance force.

[0142] In the event that it is desired that articulated arm 14 bemounted upside down such as on a grinder, beam or ceiling, theorientation of spring 110 may similarly be inverted (or reversed) sothat the proper orientation for the necessary counterbalance may beachieved.

[0143] Turning now to FIGS. 29 and 30A-C, a preferred embodiment of themeasurement probe 28 will now be described. Probe 28 includes a housing196 having an interior space 198 therein for housing printed circuitboard 118. It will be appreciated that housing 196 constitutes a dualsocket joint of the type described above and includes a socket 197 inwhich is bonded a support member 199 for supporting circuit board 118.Preferably, handle 28 includes two switches, namely a take switch 200and a confirm switch 202. These switches are used by the operator toboth take a measurement (take switch 200) and to confirm the measurement(confirm switch 202) during operation. In accordance with an importantfeature of this invention, the switches are differentiated from eachother so as to minimize confusion during use. This differentiation maycome in one or more forms including, for example, the switches 200, 202being of differing height and/or differing textures (note that switch202 has an indentation as opposed to the smooth upper surface of switch200) and/or different colors (for example, switch 200 may be green andswitch 202 may be red). Also in accordance with an important feature ofthis invention, an indicator light 204 is associated with switches 200,202 for indicating proper probing. Preferably, the indicator light 204is a two-color light so that, for example, light 204 is green upontaking of a measurement (and pressing the green take button 200) and isred for confirming a measurement (and pressing the red button 202). Theuse of a muticolored light is easily accomplished using a known LED asthe light source for light 204. To assist in gripping, to provideimproved aesthetics and for impact resistance, an outer protectingcovering of the type described above is identified at 206 and providedover a portion of probe 28. A switch circuit board 208 is provided forthe mounting of buttons 200, 202 and lamp 204 and is supported bysupport member 199. Switch board 208 is electrically interconnected withboard 118 which houses components for processing the switches and lightindicator as well as for the processing of short hinge joint 36.

[0144] In accordance with another important feature of the presentinvention, and with reference to both FIG. 29 as well as FIGS. 30A-C,probe 28 includes a permanently installed touch trigger probe as well asa removable cap for adapting a fixed probe while protecting the touchtrigger probe. The touch probe mechanism is shown at 210 in FIG. 29 andis based on a simplified three point kinematics seat. This conventionalconstruction comprises a nose 212 which contacts a ball 214 biased by acontact spring 216. Three contact pins (one pin being shown at 218) arein contact with an underlying electric circuit. Application of anyforces against the probe nose 212 results in lifting of any one of thethree contact pins 218 resulting in an opening of the underlyingelectric circuit and hence activation of a switch. Preferably, touchtrigger probe 210 will operate in conjunction with the front “take”switch 200.

[0145] As shown in FIG. 30B, when using touch trigger probe 210, aprotective threaded cover 220 is threadably attached to threading 222surrounding trigger probe 210. However, when it is desired to use afixed probe rather than the touch trigger probe, the removable cap 220is removed and a desired fixed probe such as that shown at 224 in FIGS.29 and 30A-C is threadably attached to threading 222. It will beappreciated that while fixed probe 224 has a round ball 226 attachedthereto, any different and desired fixed probe configuration may beeasily threadably attached to probe 28 via threading 222. Touch triggerprobe assembly 210 is mounted in a housing 228 which is threadablyreceived into threaded connector 230 which forms a part of probe housing196. This threadable interconnection provides for the full integrationof touch trigger probe 210 into probe 28. The provision of a fullyintegrated touch probe represents an important feature of the presentinvention and is distinguishable from prior art detachable touch probesassociated with prior art CMMs. In addition, the permanently installedtouch trigger probe is also easily convertible to a hard probe asdescribed above.

[0146] FIGS. 29A-C disclose yet another preferred embodiment for ameasurement probe in accordance with the present invention. In FIGS.29A-C, a measurement probe is shown at 28′ and is substantially similarto measurement probe 28 in FIG. 29 with the primary difference residingin the configuration of the “take” and “confirm” switches. Rather thanthe discrete button type switches shown in FIG. 29, measurement probe28′ utilizes two pairs of arcuate oblong switches 200 a-b and 202 a-b.Each respective pair of oblong switches 202 a-b and 200 a-b correspondrespectively to the take switch and the confirm switch as describedabove with respect to FIG. 29. An advantage of the measurement probe 28′embodiment relative to the measurement probe 28 embodiment is that eachpair of oblong switches 202 and 200 surround virtually the entirecircumference (or at least the majority of the circumference) of themeasurement probe and therefore are more easily actuatable by theoperator of the portable CMM. As in the FIG. 29 embodiment, an indicatorlight 204 is associated with each switch with the light 204 and switches200, 202 being mounted on respective circuit boards 208′. Also, as inthe FIG. 29 embodiment, switches 200, 202 may be differentiated usingfor example, different heights, different textures and/or differentcolors. Preferably, switches 200, 202 have a slight float such that thebutton may be actuated when pressed down in any location therealong. Asin the FIG. 29 embodiment, an outer protective covering of the typedescribed above is used at 206 and provided over a portion of probe 28′.

[0147] Referring now to FIG. 31, an alternative measurement probe foruse with CMM 10 is shown generally at 232. Measurement probe 232 issimilar to measurement probe 28 of FIG. 29 with the primary differencebeing that probe 232 includes a rotating handle cover 234. Rotatingcover 234 is mounted on a pair of spaced bearings 236, 238 which in turnare mounted on an inner core or support 240 such that cover 234 isfreely rotatable (via bearings 236, 238) about inner core 240. Bearings236, 238 are preferably radial bearings and minimize the parasitictorques on the arm due to probe handling. Significantly, the switchplate 208′ and corresponding switches 200′, 202′ and LED 204′ are allmounted to rotating handle cover 234 for rotation therewith. Duringrotation, electrical connectivity to processing circuit board 118′ isprovided using a conventional slip ring mechanism 242 which comprises aknown plurality of spaced spring fingers 242 which contact stationarycircular channels 244. In turn, these contact channels 244 areelectrically connected to circuit board 118′. The rotating handle cover234 and switch assembly is thus electrically coupled to the inner coreor probe shaft 240 and electronics board 118′ using the slip ringconductor 242. The rotation of the probe handle 234 permits switches200′, 202′ to be oriented conveniently for the user. This allows thearticulated arm 14′ to measure accurately during handling by minimizingundocumented forces. The cover 234 is preferably comprised of a rigidpolymer and is provided with appropriate indentations 246 and 248 toallow easy and convenient gripping and manipulation by the probeoperator.

[0148] It will be appreciated that the remainder of probe 232 is quitesimilar to probe 28 including the provision of a permanently andintegrally installed touch probe 210 in cover 220. Note that switches200′, 202′ are of differing heights and surface textures so as toprovide ease of identification.

[0149] The rotating cover 234 is a significant advance in the CMM fieldin that it can alleviate the need for a seventh axis of rotation at theprobe such as disclosed in aforementioned U.S. Pat. No. 5,611,147. Itwill be appreciated that the addition of a seventh axis leads to a morecomplex and expensive CMM as well as the addition of possible error intothe system. The use of the rotatable probe 232 alleviates the need for a“true” seventh axis as it permits the probe to provide the rotationneeded for handle position at the probe end without the complexity of aseventh transducer and associated bearings, encoder and electronics.

[0150] In the event that it is desired to utilize a measurement probehaving a “true” seventh axis, that is, having a measurement probe with aseventh rotary encoder for measuring rotary rotation, such a measurementprobe is shown in FIGS. 37-40. With reference to such FIGURES, ameasurement probe 500 is shown with such measurement probe beingsubstantially similar to the measurement probe in FIG. 29 with theprimary difference being the insertion of a modular bearing/transducercartridge 502 of the type described above, the presence of the take andconfirm switches 504, 506 on the sides of the measurement probe and theinclusion of a removable handle 508.

[0151] It will be appreciated that the modular bearing/transducercartridge 502 is substantially similar to the cartridges described indetail above and include a rotatable shaft, a pair of bearings on theshaft, an optical encoder disk, at least one and preferably two opticalread heads spaced from and in optical communication with the encoderdisk and a housing surrounding the bearings, optical encoder disk, readhead(s) and at least a portion of the shaft so as to define the discretemodular bearing/transducer cartridge. A circuit board 503 for theencoder electronics resides in an opening 504 with probe 500. Pairs oftake and confirm buttons 504, 506 are positioned on either side of adownwardly projected housing portion 510 of probe 500 with the buttonsbeing connected to an appropriate PC board 512 as in the measurementprobe of the FIG. 29 embodiment. Similarly, an indicator light 513 ispositioned between buttons 504, 506 as in the previously discussedembodiments. A pair of threaded openings 514 in housing 510 receivefasteners for removable attachment of handle 508 which provides for easeof rotary manipulation during use of measurement probe 500.

[0152] In all other substantial respects, measurement probe 500 issimilar to measurement probe 28 of FIG. 29 including the preferred useof permanently installed touch trigger probe at 516 as well as aremovable cap for adapting a fixed probe 518 while protecting the touchtrigger probe. It will be appreciated that the seventh rotary encoder502 included in measurement probe 500 facilitates the use of CMM 10 inconnection with known laser line scanners and other peripheral devices.

[0153] Turning now to FIGS. 2-4, 23 and 25, in accordance with animportant feature of the present invention, a portable power supply isprovided to power CMM 10 thus providing a fully portable CMM. This is incontrast to prior art CMMs where power supply was based only on an ACcord. In addition, CMM 10 may also be powered directly by an AC cordthrough an AC/DC adapter via a conventional plug-in socket. As shown inFIGS. 2, 3 and 25, a conventional rechargeable battery (e.g., Li-ionbattery) is shown at 22. Battery 22 is mechanically and electricallyconnected into a conventional battery support 252 which in turn iselectrically connected to a conventional power supply and batteryrecharger circuit component 254 located on circuit board 20. Alsocommunicating with board 20 is an on/off switch 258 (see FIG. 3) and ahigh-speed communication port 260 (preferably a USB port). The jointelectronics of arm 14 is connected to board 20 using an RS-485 bus.Battery 22 can be charged on a separate charger, or charged in place incradle 252 as is commonly found in conventional video cameras. It willbe appreciated that portable computer 172 (see FIG. 2) can operate forseveral hours on its built-in batteries and/or in the alternative, maybe electrically connected to the power supply unit 254 of CMM 10.

[0154] The on-board power supply/recharger unit in accordance with thepresent invention is preferably positioned as an integral part of CMM 10by locating this component as an integral part of base 12 and morespecifically as a part of the plastic base housing 26A, B. Note alsothat preferably, base housing 26A, B includes a small storage area 259having a pivotable lid 262 for storing spare batteries, probes, or thelike.

[0155] Turning now to FIGS. 4, 25 and 32-34, the novel magnetic mountingdevice for use with CMM 10 will now be described. This magnetic mountingdevice is shown generally at 24 in FIGS. 4, 25, 32 and 33. Magneticmount 24 includes a cylindrical non-magnetic housing 266 whichterminates at its upper end in a threaded section 268. As with all ofthe preferred threading used in CMM 10, threading 268 is a taperedthread which is intended to be threadingly connected to threading 126 offirst long joint 16 as best shown in FIG. 25. Non-magnetic housing 266has a substantially cylindrical configuration with the exception of twolongitudinal extensions 270, 272 which are opposed from each other at180o and extend outwardly and downwardly from housing 266. Attached oneither side of longitudinal extensions 270, 272 are a pair ofsemi-cylindrical housings 274, 276, each of which is formed from a“magnetic” material, that is, a material capable of being magnetizedsuch as iron or magnetic stainless steel. Together, “magnetic” housinghalves 274, 276 and longitudinal extensions 270, 272 form an open endedcylindrical enclosure for receiving and housing a magnetic core 278.Magnetic core 278 has an oblong shape with a non-magnetic center 280sandwiched between a pair of rare earth magnets (e.g.,neodymium-iron-boron) 282, 284. An axial opening 286 is provided throughnon-magnetic center 280. A circular cover plate 288 is positionedbeneath magnetic core 278 and located within the lower housing formed byelements 274, 276 and longitudinal extensions 270, 272. A shaft 290 ispositioned through a circular opening 292 in housing 266 and extendsdownwardly through axial opening 286 of magnetic core 278. Shaft 290 issupported for rotation by an upper bearing 292 and a lower bearing 294.Upper bearing 292 is received by an internal cylindrical recess inhousing 266 and lower bearing 294 is received by a similar cylindricalrecess in cover plate 288. A lever 296 extends outwardly andperpendicularly from shaft 290 and, as will be described hereafter,provides an on/off mechanism for the magnetic mount 264. Lever 296extends outwardly of housing 266 through a groove 297 through housing266 (see FIG. 25).

[0156] This entire assembly of lever 296, shaft 290 and bearings 292,294 is secured together using an upper threaded fastener 298 and a lowerretaining ring 300. It will be appreciated that the various componentsof magnetic mount 264 are further secured by, for example, threadedfasteners 302 which connect housing 266 to “magnetic” material housingportions 274, 276 and threaded fasteners 304 which interconnect housingportions 274, 276 to cover 288. In addition, threaded fasteners 306attached longitudinal extensions 270, 272 of housing 266 to cover 288. Apin 308 is received by a lateral opening in core 278 and a lateralopening in shaft 290 so as to lock shaft 290 to core 278. In this way,as lever 296 is rotated, shaft 290 will rotate core 278 via shaftconnection 208.

[0157] As shown in FIGS. 1, 3 and 25, lever 296 is connected to a handle310 which is easily accessible on the exterior of base 12 and is used toactuate magnetic mount 264. To accomplish such actuation, handle 296 issimply moved (from the right to the left in FIG. 1). Movement of handle310 will in turn rotate lever 296 which in turn will rotate shaft 290which will then rotate rare earth magnets 282, 284 from theirnon-operative position (wherein magnets 282, 284 are aligned withnon-magnetic extensions 270, 272) into an actuated position wheremagnets 282, 284 are aligned with magnetic material 274, 276. When themagnets are aligned with the magnetic material as described, a magneticfield (flux) is formed. Similarly, when the magnets 282, 284 are out ofalignment with the magnetic material 274, 276, the flux path isinterrupted. In this state, the magnetic base can be separated from thetable upon which it sits. Note however that even in the non-alignedposition, there will be some residual magnetic flux. This small residualmagnetic flux in the “off” position is a positive feature of thisinvention as a small amount of magnetic flux acts to react with themagnet and automatically rotate lever 296 back to the “on” position whenreplaced on the table. It will be appreciated that when the magnets arein alignment with the magnetic material, a strong magnetic field will beestablished and semi-circular elements 274, 276 will be magneticallyadhered to the annular surface formed at the bottom thereof as shown at312 in FIGS. 25 and 33.

[0158] The magnetic mount 264 of the present invention provides a fullyintegrated yet removable mounting device since it is detachably mounted(via threading 268) and may be replaced by other attachments such as ascrew mount or vacuum mount. Of course, in order to be properly used,magnetic mount 264 must be placed on a magnetizable surface and beactivated (via lever 296) in order to operate. In the event thatmounting is required to a non-magnetic surface (e.g., granite), theninterface plates or other suitable mechanisms must be used between themagnetic base and the non-magnetic surface.

[0159] While preferred embodiments have been shown and described,various modifications and substitutions may be made thereto withoutdeparting from the spirit and scope of the invention. Accordingly, it isto be understood that the present invention has been described by way ofillustrations and not limitation.

What is claimed is:
 1. A portable coordinate measurement machine (CMM)for measuring the position of an object in a selected volume,comprising: a manually positionable articulated arm having opposed firstand second ends, said arm including a plurality of joints; a measurementprobe attached to a first end of said articulated arm; an electroniccircuit which receives the position signals from transducers in said armand provides a digital coordinate corresponding to the position of theprobe in a selected volume; and wherein at least one of said jointsfurther comprise; a periodic pattern of a measurable characteristic; atleast one read head spaced from and in communication with said pattern;said pattern and said read head being positioned within said joint so asto be rotatable with respect to each other; and at least one sensorwhich measures relative movement in said articulated arm with respect tosaid at least one read head so as to improve the measurement accuracy ofsaid at least one read head.
 2. The CMM of claim 1 wherein: said atleast one read head is in axial alignment with said at least one sensor.3. The CMM of claim 1 wherein said at least one sensor comprises aplurality of spaced sensors which measure displacement.
 4. The CMM ofclaim 1 wherein said at least one sensor comprises a sensor whichmeasures displacement.
 5. The CMM of claim 4 including at least onesensor for measuring X-axis displacement of said pattern.
 6. The CMM ofclaim 4 including at least one sensor for measuring Y-axis displacementof said pattern.
 7. The CMM of claim 5 including at least one sensor formeasuring Y-axis displacement of said pattern.
 8. The CMM of claim 1wherein said at least one joint includes a shaft surrounded, at least inpart, by a housing, said shaft and said housing being adapted to rotaterelative to one another, and wherein said at least one sensor includesat least one sensor for measuring relative movement between said shaftand said housing.
 9. The CMM of claim 8 including a plurality of sensorsfor measuring relative movement between said shaft and said housing. 10.The CMM of claim 8 wherein said shaft is rotatable.
 11. The CMM of claim9 wherein said shaft is rotatable.
 12. The CMM of claim 11 wherein saidat least one sensor includes: at least two sensors for measuringrelative movement of said shaft including a first sensor for measuring Xaxis displacement and a second sensor for measuring Y axis displacement.13. The CMM of claim 12 wherein said plurality of sensors for measuringrelative movement of said shaft further include a third sensor formeasuring X axis rotation, a fourth sensor for measuring Y axis rotationand a fifth sensor for measuring Z axis displacement.
 14. The CMM ofclaim 12 wherein said at least one read head measures Z axis rotation ofsaid shaft.
 15. The CMM of claim 13 wherein said at least one read headmeasures Z axis rotation of said shaft.
 16. The CMM of claim 13 whereinsaid third, fourth and fifth sensors are positioned at about 120 degreeswith respect to each other. 17 The CMM of claim 8 including at leastfive sensors which, together with said read head, measure at least sixdegrees of freedom of said shaft.
 18. The CMM of claim 1 wherein saidrelative movement is caused by deformation to said arm.
 19. The CMM ofclaim 18 wherein said relative movement is caused by deformation ofbearings in said joints.
 20. The CMM of claim 1 wherein said at leastone sensor includes: at least two sensors which measure movement in saidperiodic pattern with respect to said at least one read head.
 21. TheCMM of claim 20 wherein: said at least two sensors are positioned atabout 90 degrees to each other.
 22. The CMM of claim 21 wherein: said atleast two sensors comprise proximity sensors.
 23. The CMM of claim 1wherein: said pattern comprises an optical fringe pattern; and said atleast one read head comprises an optical read head.
 24. The CMM of claim23 wherein: said optical fringe pattern is disposed on an opticalencoder disk.
 25. The CMM of claim 23 wherein said communicationcomprises: said read head detecting the interference between diffractionorders to produce sinusoidal signals from said read head inserted insaid fringe pattern, said sinusoidal signals being electronicallyinterpolated to detect displacement.
 26. The CMM of claim 1 wherein:said pattern of a measurable characteristic is at least one of thecharacteristics selected from the group consisting of reflectivity,opacity, magnetic field, capacitance, inductance and surface roughness.27. The CMM of claim 1 wherein said joints comprise long joints forswiveling motion and short joints for hinged motion.
 28. The CMM ofclaim 27 including three joint pairs, each joint pair comprising a longjoint and a short joint.
 29. The CMM of claim 1 wherein said joints arearranged in the joint configurations selected from the group consistingof 2-2-2, 2-1-2, 2-2-3, and 2-1-3.
 30. The CMM of claim 1 wherein: saidpattern is rotatable with respect to said at least one read head; andsaid at least one read head is stationary with respect to said pattern.31. The CMM of claim 1 wherein: said pattern is stationary with respectto said at least one read head; and said at least one read head isrotatable with respect to said pattern.
 32. The CMM of claim 1 whereinsaid joint further comprises: a first and second housing, and arotatable shaft extending from said second housing into said firsthousing; a bearing disposed between said shaft and said first housingpermitting said rotatable shaft to rotate within said first housing;said pattern being attached to said rotatable shaft; said at least oneread head being fixed within said first housing such that rotation ofthe first housing with respect to the second housing causes said atleast one read head to move relative to said pattern.
 33. The CMM ofclaim 32 wherein: said pattern is attached directly to said shaft. 34The CMM of claim 1 wherein said at least one joint comprises: a firsthousing; a second housing; a rotatable shaft fixed to said secondhousing and extending into said first housing; at least one bearingsupported within said first housing and supporting said rotatable shaftfor rotation about its axis; wherein one of said pattern and said atleast one read head is fixed to an end of said shaft and the other ofsaid pattern and said at least one read head is fixed within said firsthousing.
 35. The CMM of claim 4 wherein said at least one sensorcomprises a proximity sensor.
 36. The CMM of claim 35 wherein saidproximity sensor measures movement using at least one of Hall effects,magneto effects, resistive effects, capacitance and optics.
 37. Aportable coordinate measurement machine (CMM) for measuring the positionof an object in a selected volume, comprising: a manually positionablearticulated arm having opposed first and second ends, said arm includinga plurality of joints; a measurement probe attached to a first end ofsaid articulated arm; an electronic circuit which receives the positionsignals from transducers in said arm and provides a digital coordinatecorresponding to the position of the probe in a selected volume; andwherein at least one of said joints further comprise; a rotatable shaftsurrounded, at least in part, by a housing, said shaft and said housingbeing adapted to rotate relative to one another; a periodic pattern of ameasurable characteristic; at least one read head spaced from and incommunication with said pattern; said pattern and said read head beingpositioned within said joint so as to be rotatable with respect to eachother; and a plurality of displacement sensors which measure relativemovement between said shaft and said housing, said relative movementmeasurement being used to improve the measurement accuracy of said atleast one read head.
 38. The CMM of claim 37 including at least fivesensors which, together with said read head, measure at least sixdegrees of freedom of said shaft.